1. Field of the Invention
The present invention relates to a declutching device for a clutch, in particular for a mechanical diaphragm clutch for a motor vehicle.
More particularly, the invention relates to a hydraulically controlled declutching device comprising a clutch release bearing which is adapted to act on the declutching device of the clutch, such as a diaphragm, and carried by a piston which is mounted for axial movement, an axially oriented blind cavity defined between a part, referred to as the fixed part and comprising an external body and an internal tube guide which are mounted concentrically, wherein the piston slides axially along the tube guide and penetrates into the blind cavity so as to define with the piston a variable volume chamber.
The invention also relates to a method of making the tube guide.
2. Description of the Related Art A declutching device of this kind with hydraulic control through the piston is described in the document FR-A-2 730 532.
In the latter, the blind cavity is bounded by the tube guide, or guide tube, and by the external body.
The said tube has a plate portion at its rear end. The plate portion is gripped between the external body and the fixed part.
A seal is interposed between the plate portion of the tube guide and the external body, so as to seal the cavity. The axially oriented annular blind cavity is therefore difficult to standardise. In order to overcome this drawback in a simple and inexpensive way, recourse may be considered to a solution of the same type as that described in the document FR-A-2 531 164, that is to say delimiting the axially oriented blind annular cavity by the guide tube, which for this purpose has a base portion that joins an outer tube to an inner tube, which has the greater length.
This may be achieved by press-forming from sheet metal.
Such an arrangement is not entirely satisfactory because the coaxiality between the outer tube and the inner tube is not as good as is desired. In addition, the inner and outer faces of the inner and outer tubes respectively are not as smooth as desired.